(CNN) -- The runner-up in Honduras' presidential election says she will not recognize the outcome and is demanding a vote-by-vote recount.
The strong allegations of fraud by Xiomara Castro, the wife of ousted former President Manuel Zelaya, raise the possibility of political unrest in the Central American country.
The leftist candidate says her political party has uncovered evidence of fraud and vows to challenge the triumph of ruling party candidate Juan Orlando Hernandez.
With 80% of votes counted, electoral officials declared Hernandez the winner with more than 35% of the vote, placing him six percentage points ahead of Castro.
Castro had been mostly quiet since election night. Friday was her first public appearance since the vote.
"I am here, once again before you, to reiterate that we have found countless evidence of the disgusting monstrosity with which they are robbing the presidency from our people," she said.
International election observers have said there were some irregularities, but in general agreed that the elections were transparent.
The U.S. State Department noted that the Organization of American States and European Union observers reported a clean election.
"We support the ongoing work of (electoral officials) and the political parties to finalize the results and resolve inconsistencies in a transparent manner and urge the Honduran people to continue to demonstrate their respect for rule of law and peaceful, democratic processes," State Department spokeswoman Jen Psaki said.
Castro said she would not back down from her challenge and accused the ruling party of rigging the system to help their candidate.
"We reject the legitimacy of any government that is the product of this suffocating assault," she said.
Following her husband's ouster in a 2009 coup, Castro founded the Liberty and Refoundation Party (LIBRE) on a platform that carried on her husband's projects and found herself at the top of some polls. A victory by Castro would have been a remarkable comeback for Zelaya back to the presidential palace, even as a first husband.